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Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format |
Date: |
Mon, 27 Sep 2010 11:15:14 +0100 |
On Mon, Sep 27, 2010 at 11:13 AM, Avi Kivity <address@hidden> wrote:
> On 09/23/2010 05:41 PM, Stefan Hajnoczi wrote:
>>
>> QEMU Enhanced Disk format is a disk image format that forgoes features
>> found in qcow2 in favor of better levels of performance and data
>> integrity. Due to its simpler on-disk layout, it is possible to safely
>> perform metadata updates more efficiently.
>>
>> Installations, suspend-to-disk, and other allocation-heavy I/O workloads
>> will see increased performance due to fewer I/Os and syncs. Workloads
>> that do not cause new clusters to be allocated will perform similar to
>> raw images due to in-memory metadata caching.
>>
>> The format supports sparse disk images. It does not rely on the host
>> filesystem holes feature, making it a good choice for sparse disk images
>> that need to be transferred over channels where holes are not supported.
>>
>> Backing files are supported so only deltas against a base image can be
>> stored.
>>
>> The file format is extensible so that additional features can be added
>> later with graceful compatibility handling.
>>
>> Internal snapshots are not supported. This eliminates the need for
>> additional metadata to track copy-on-write clusters.
>>
>> Compression and encryption are not supported. They add complexity and can
>> be
>> implemented at other layers in the stack (i.e. inside the guest or on the
>> host). Encryption has been identified as a potential future extension and
>> the
>> file format allows for this.
>>
>
> IMO the file format should be part of this patchset. Wikis are nice but
> they aren't a good place for authoritative documentation.
Good idea. Will add the specification in v2.
Stefan
- Re: [Qemu-devel] [PATCH 1/7] qcow2: Make get_bits_from_size() common, (continued)
[Qemu-devel] [PATCH 2/7] cutils: Add bytes_to_str() to format byte values, Stefan Hajnoczi, 2010/09/23
[Qemu-devel] [PATCH 4/7] qed: Add QEMU Enhanced Disk image format, Stefan Hajnoczi, 2010/09/23
[Qemu-devel] [PATCH 6/7] qed: Read/write support, Stefan Hajnoczi, 2010/09/23
Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/27
Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/27
- Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format,
Stefan Hajnoczi <=